In 802.11 specifications, one AP and multiple STAs associated with the AP constitute a basic service set (BSS).
In a BSS, an uplink multiuser data transmission method includes that on a single channel or multiple channels, after an AP sends a trigger frame, after a time of Short Interframe Space (SIFS), if the channel is idle, a STA randomly selects a sub-channel to send a request to send (RTX) to contend for access. After the RTX is received, after a time of SIFS, the AP sends a clear to send (CTX) message to the STA on a whole channel to schedule the STA to transmit data on a specific sub-channel. After the AP sends the CTX, after a time of SIFS, the STA sends uplink data on an allocated sub-channel, and then after a time of SIFS, the AP replies with an acknowledgement message on the whole channel. However, the uplink multiuser data transmission method has the following disadvantages: 1) Because before a Trigger frame is used to schedule multiple users, an AP does not know which users have uplink data, a problem of “triggering without response” exists; 2) when a STA performs uplink data transmission, multiple STAs distributed relatively broadly in geographic positions may perform access in parallel, causing a problem of interference diffusion; 3) an effect of “proximity” exists, and relatively complex power control may be needed.
Another uplink multiuser data transmission method is on a single channel or multiple channels; all STAs listen to channels and back off independently, and after backing off, randomly select sub-channels to send RTXs to contend for channel access. After an AP receives the RTX, after a time of SIFS, the AP sends CTXs to the STAs on a whole channel to schedule the STAs to transmit data on specific sub-channels. After the AP sends the CTXs, after a time of SIFS, the STAs send data on allocated sub-channels, and then after a time of SIFS, the AP replies with an acknowledgement message on a whole channel. However, the uplink multiuser data transmission method can hardly resolve a problem of RTX sending synchronization between STAs, causing a problem of mutual interference between multiple channels and reducing the uplink access efficiency.